bims-mikwok 2022-08-07 papers

bims-mikwok

Biomed News

on Mitochondrial quality control

Issue of 2022‒08‒07
nine papers selected by
Avinash N. Mukkala, University of Toronto

CMT2A-linked mitochondrial hyperfusion-driving mutant MFN2 perturbs ER-mitochondrial associations and Ca2+ homeostasis.
Nrf2 as a regulator of mitochondrial function: Energy metabolism and beyond.
Regulation of mitochondrial proteostasis by the proton gradient.
Cleavage of mitochondrial homeostasis regulator PGAM5 by the intramembrane protease PARL is governed by transmembrane helix dynamics and oligomeric state.
Acute exercise dynamically modulates the hepatic mitochondrial proteome.
Measuring Single-Cell Mitochondrial DNA Copy Number and Heteroplasmy using Digital Droplet Polymerase Chain Reaction.
Mitochondrial remodeling and ischemic protection by G protein-coupled receptor 35 agonists.
Highly conserved shifts in ubiquitin-proteasome system (UPS) activity drive mitochondrial remodeling during quiescence.
The role of mitochondrial energetics in the origin and diversification of eukaryotes.

Biol Cell. 2022 Aug 04.

CMT2A-linked mitochondrial hyperfusion-driving mutant MFN2 perturbs ER-mitochondrial associations and Ca2+ homeostasis.

Rajdeep Das, Subhrangshu Das, Saikat Chakrabarti, Oishee Chakrabarti.

  Mitofusin2 (MFN2), an important molecular player that regulates mitochondrial fusion, also helps maintain the inter-organellar contact sites, referred as mitochondria associated membranes (MAMs) that exist between the ER and mitochondria. Here we show that a mutant of MFN2, R364W-MFN2, linked with the Charcot Marie Tooth disease, promotes mitochondrial hyperfusion, alters ER mitochondrial associations at the MAM junctions and perturbs inter-organellar calcium homeostasis. Such hyperfused mitochondria are also predisposed towards stress and undergo rapid fission upon induction of mild stress. Thus, here we report that presence of the R364W-MFN2 mutation makes cells susceptible towards stress, thus negatively affecting cellular health. This article is protected by copyright. All rights reserved.

Keywords:  CMT2A-linked MFN2 mutant; DRP1; ER-mitochondrial associations; mitochondrial hyperfusion

DOI:  https://doi.org/10.1111/boc.202100098
Free Radic Biol Med. 2022 Jul 30. pii: S0891-5849(22)00496-8. [Epub ahead of print]

Nrf2 as a regulator of mitochondrial function: Energy metabolism and beyond.

Noemí Esteras, Andrey Y Abramov.

  Mitochondria are unique and essential organelles that mediate many vital cellular processes including energy metabolism and cell death. The transcription factor Nrf2 (NF-E2 p45-related factor 2) has emerged in the last few years as an important modulator of multiple aspects of mitochondrial function. Well-known for controlling cellular redox homeostasis, the cytoprotective effects of Nrf2 extend beyond its ability to regulate a diverse network of antioxidant and detoxification enzymes. Here, we review the role of Nrf2 in the regulation of mitochondrial function and structure. We focus on Nrf2 involvement in promoting mitochondrial quality control and regulation of basic aspects of mitochondrial function, including energy production, reactive oxygen species generation, calcium signalling, and cell death induction. Given the importance of mitochondria in the development of multiple diseases, these findings reinforce the pharmacological activation of Nrf2 as an attractive strategy to counteract mitochondrial dysfunction.

Keywords:  Calcium; Dynamics; Energy; Fission; Fusion; Mitochondria; Mitochondrial biogenesis; Mitophagy; Nrf2; ROS; mPTP

DOI:  https://doi.org/10.1016/j.freeradbiomed.2022.07.013
EMBO J. 2022 Aug 01. e110476

Regulation of mitochondrial proteostasis by the proton gradient.

Maria Patron, Daryna Tarasenko, Hendrik Nolte, Lara Kroczek, Mausumi Ghosh, Yohsuke Ohba, Yvonne Lasarzewski, Zeinab Alsadat Ahmadi, Alfredo Cabrera-Orefice, Akinori Eyiama, Tim Kellermann, Elena I Rugarli, Ulrich Brandt, Michael Meinecke, Thomas Langer.

  Mitochondria adapt to different energetic demands reshaping their proteome. Mitochondrial proteases are emerging as key regulators of these adaptive processes. Here, we use a multiproteomic approach to demonstrate the regulation of the m-AAA protease AFG3L2 by the mitochondrial proton gradient, coupling mitochondrial protein turnover to the energetic status of mitochondria. We identify TMBIM5 (previously also known as GHITM or MICS1) as a Ca2+ /H+ exchanger in the mitochondrial inner membrane, which binds to and inhibits the m-AAA protease. TMBIM5 ensures cell survival and respiration, allowing Ca2+ efflux from mitochondria and limiting mitochondrial hyperpolarization. Persistent hyperpolarization, however, triggers degradation of TMBIM5 and activation of the m-AAA protease. The m-AAA protease broadly remodels the mitochondrial proteome and mediates the proteolytic breakdown of respiratory complex I to confine ROS production and oxidative damage in hyperpolarized mitochondria. TMBIM5 thus integrates mitochondrial Ca2+ signaling and the energetic status of mitochondria with protein turnover rates to reshape the mitochondrial proteome and adjust the cellular metabolism.

Keywords:  AFG3L2; TMBIM5; mitochondrial calcium; proton gradient; respiratory chain

DOI:  https://doi.org/10.15252/embj.2021110476
J Biol Chem. 2022 Jul 31. pii: S0021-9258(22)00763-3. [Epub ahead of print] 102321

Cleavage of mitochondrial homeostasis regulator PGAM5 by the intramembrane protease PARL is governed by transmembrane helix dynamics and oligomeric state.

Verena Siebert, Mara Silber, Elena Heuten, Claudia Muhle-Goll, Marius K Lemberg.

  The intramembrane protease PARL acts as a crucial mitochondrial safeguard by cleaving the mitophagy regulators PINK1 and PGAM5. Depending on the stress level, PGAM5 can either stimulate cell survival or cell death. In contrast to PINK1, which is constantly cleaved in healthy mitochondria and only active when the inner mitochondrial membrane is depolarized, PGAM5 processing is inversely regulated. However, determinants of PGAM5 that indicate it as a conditional substrate for PARL have not been rigorously investigated, and it is unclear how uncoupling the mitochondrial membrane potential affects its processing compared to that of PINK1. Here, we show that several polar transmembrane residues in PGAM5 distant from the cleavage site serve as key determinants for its PARL-catalyzed cleavage. Our NMR analysis indicates that a short N-terminal amphipathic helix, followed by a kink and a C-terminal transmembrane helix harboring the scissile peptide bond, are key for a productive interaction with PARL. Furthermore, we also show that PGAM5 is stably inserted into the inner mitochondrial membrane until uncoupling the membrane potential triggers its disassembly into monomers, which are then cleaved by PARL. In conclusion, we propose a model in which PGAM5 is slowly processed by PARL-catalyzed cleavage that is influenced by multiple hierarchical substrate features, including a membrane potential-dependent oligomeric switch.

Keywords:  PGAM5; helix dynamics; intramembrane proteolysis; oligomeric state; rhomboid serine protease

DOI:  https://doi.org/10.1016/j.jbc.2022.102321
Mol Omics. 2022 Aug 05.

Acute exercise dynamically modulates the hepatic mitochondrial proteome.

Colin S McCoin, Edziu Franczak, Michael P Washburn, Mihaela E Sardiu, John P Thyfault.

Exercise powerfully increases energy metabolism and substrate flux in tissues, a process reliant on dramatic changes in mitochondrial energetics. Liver mitochondria play a multi-factorial role during exercise to fuel hepatic glucose output. We previously showed acute exercise activates hepatic mitophagy, a pathway to recycle low-functioning/damaged mitochondria, however little is known how individual bouts of exercise alters the hepatic mitochondrial proteome. Here we leveraged proteomics to examine changes in isolated hepatic mitochondria both immediately after and 2 hours post an acute, 1 hour bout of treadmill exercise in female mice. Further, we utilized leupeptin, a lysosomal inhibitor, to capture and measure exercise-induced changes in mitochondrial proteins that would have been unmeasured due to their targeting for lysosomal degradation. Proteomic analysis of enriched hepatic mitochondria identified 3241 total proteins. Functional enrichment analysis revealed robust enrichment for proteins critical to the mitochondria including metabolic pathways, tricarboxylic acid cycle, and electron transport system. Compared to the sedentary condition, exercise elevated processes regulating lipid localization, Il-5 signaling, and protein phosphorylation in isolated mitochondria. t-SNE analysis identified 4 unique expressional clusters driven by time-dependent changes in protein expression. Isolation of proteins significantly altered with exercise from each cluster revealed influences of leupeptin and exercise both independently and cooperatively modulating mitochondrial protein expressional profiles. Overall, we provide evidence that acute exercise rapidly modulates changes in the proteins/pathways of isolated hepatic mitochondria that include fatty acid metabolism/storage, post-translational protein modification, inflammation, and oxidative stress. In conclusion, the hepatic mitochondrial proteome undergoes extensive remodeling with a bout of exercise.

DOI: https://doi.org/10.1039/d2mo00143h
J Vis Exp. 2022 Jul 12.

Measuring Single-Cell Mitochondrial DNA Copy Number and Heteroplasmy using Digital Droplet Polymerase Chain Reaction.

Stephen P Burr, Patrick F Chinnery.

The mammalian mitochondrial (mt)DNA is a small, circular, double-stranded, intra-mitochondrial DNA molecule, encoding 13 subunits of the electron transport chain. Unlike the diploid nuclear genome, most cells contain many more copies of mtDNA, ranging from less than 100 to over 200,000 copies depending on cell type. MtDNA copy number is increasingly used as a biomarker for a number of age-related degenerative conditions and diseases, and thus, accurate measurement of the mtDNA copy number is becoming a key tool in both research and diagnostic settings. Mutations in the mtDNA, often occurring as single nucleotide polymorphisms (SNPs) or deletions, can either exist in all copies of the mtDNA within the cell (termed homoplasmy) or as a mixture of mutated and WT mtDNA copies (termed heteroplasmy). Heteroplasmic mtDNA mutations are a major cause of clinical mitochondrial pathology, either in rare diseases or in a growing number of common late-onset diseases such as Parkinson's disease. Determining the level of heteroplasmy present in cells is a critical step in the diagnosis of rare mitochondrial diseases and in research aimed at understanding common late-onset disorders where mitochondria may play a role. MtDNA copy number and heteroplasmy have traditionally been measured by quantitative (q)PCR-based assays or deep sequencing. However, the recent introduction of ddPCR technology has provided an alternative method for measuring both parameters. It offers several advantages over existing methods, including the ability to measure absolute mtDNA copy number and sufficient sensitivity to make accurate measurements from single cells even at low copy numbers. Presented here is a detailed protocol describing the measurement of mtDNA copy number in single cells using ddPCR, referred to as droplet generation PCR henceforth, with the option for simultaneous measurement of heteroplasmy in cells with mtDNA deletions. The possibility of expanding this method to measure heteroplasmy in cells with mtDNA SNPs is also discussed.

DOI: https://doi.org/10.3791/63870
Science. 2022 Aug 05. 377(6606): 621-629

Mitochondrial remodeling and ischemic protection by G protein-coupled receptor 35 agonists.

Gregory A Wyant, Wenyu Yu, IIias P Doulamis, Rio S Nomoto, Mossab Y Saeed, Thomas Duignan, James D McCully, William G Kaelin.

Kynurenic acid (KynA) is tissue protective in cardiac, cerebral, renal, and retinal ischemia models, but the mechanism is unknown. KynA can bind to multiple receptors, including the aryl hydrocarbon receptor, the a7 nicotinic acetylcholine receptor (a7nAChR), multiple ionotropic glutamate receptors, and the orphan G protein-coupled receptor GPR35. Here, we show that GPR35 activation was necessary and sufficient for ischemic protection by KynA. When bound by KynA, GPR35 activated Gi- and G12/13-coupled signaling and trafficked to the outer mitochondria membrane, where it bound, apparantly indirectly, to ATP synthase inhibitory factor subunit 1 (ATPIF1). Activated GPR35, in an ATPIF1-dependent and pertussis toxin-sensitive manner, induced ATP synthase dimerization, which prevented ATP loss upon ischemia. These findings provide a rationale for the development of specific GPR35 agonists for the treatment of ischemic diseases.

DOI: https://doi.org/10.1126/science.abm1638
Nat Commun. 2022 Aug 01. 13(1): 4462

Highly conserved shifts in ubiquitin-proteasome system (UPS) activity drive mitochondrial remodeling during quiescence.

Sibiao Yue, Lei Wang, George N DeMartino, FangZhou Zhao, Yi Liu, Matthew H Sieber.

Defects in cellular proteostasis and mitochondrial function drive many aspects of infertility, cancer, and other age-related diseases. All of these conditions rely on quiescent cells, such as oocytes and adult stem cells, that reduce their activity and remain dormant as part of their roles in tissue homeostasis, reproduction, and even cancer recurrence. Using a multi-organism approach, we show that dynamic shifts in the ubiquitin proteasome system drive mitochondrial remodeling during cellular quiescence. In contrast to the commonly held view that the ubiquitin-proteasome system (UPS) is primarily regulated by substrate ubiquitination, we find that increasing proteasome number and their recruitment to mitochondria support mitochondrial respiratory quiescence (MRQ). GSK3 triggers proteasome recruitment to the mitochondria by phosphorylating outer membrane proteins, such as VDAC, and suppressing mitochondrial fatty acid oxidation. This work defines a process that couples dynamic regulation of UPS activity to coordinated shifts in mitochondrial metabolism in fungi, Drosophila, and mammals during quiescence.

DOI: https://doi.org/10.1038/s41467-022-32206-2
Nat Ecol Evol. 2022 Aug 01.

The role of mitochondrial energetics in the origin and diversification of eukaryotes.

Paul E Schavemaker, Sergio A Muñoz-Gómez.

The origin of eukaryotic cell size and complexity is often thought to have required an energy excess supplied by mitochondria. Recent observations show energy demands to scale continuously with cell volume, suggesting that eukaryotes do not have higher energetic capacity. However, respiratory membrane area scales superlinearly with the cell surface area. Furthermore, the consequences of the contrasting genomic architectures between prokaryotes and eukaryotes have not been precisely quantified. Here, we investigated (1) the factors that affect the volumes at which prokaryotes become surface area-constrained, (2) the amount of energy divested to DNA due to contrasting genomic architectures and (3) the costs and benefits of respiring symbionts. Our analyses suggest that prokaryotes are not surface area-constrained at volumes of 100‒103 µm3, the genomic architecture of extant eukaryotes is only slightly advantageous at genomes sizes of 106‒107 base pairs and a larger host cell may have derived a greater advantage (lower cost) from harbouring ATP-producing symbionts. This suggests that eukaryotes first evolved without the need for mitochondria since these ranges hypothetically encompass the last eukaryotic common ancestor and its relatives. Our analyses also show that larger and faster-dividing prokaryotes would have a shortage of respiratory membrane area and divest more energy into DNA. Thus, we argue that although mitochondria may not have been required by the first eukaryotes, eukaryote diversification was ultimately dependent on mitochondria.

DOI: https://doi.org/10.1038/s41559-022-01833-9